Arrangement for use in making slab ingots by electric slag-refining

ABSTRACT

The arrangement comprises an ingot mold having inside surfaces which define an elongated horizontal cross-section. The horizontal cross-section has a pair of long sides each of which has a central portion and outer portions. Fusible electrode means extend in said ingot mold and are horizontally spaced from said inside surfaces at said central portions by a larger distance than at said outer portions.

United States Patent Holzgruber et a1.

ARRANGEMENT FOR USE IN MAKING SLAB INGOTS BY ELECTRIC SLAG-REFININGInventors: Wolfgang W. Holzgruber,

Kapfenberg; Peter J. V. Machner,

Leoben; Ludwig Schwarz, Kapfenberg, all of Austria Assignee: Gebr.Bohler & Co. AG., Vienna,

Kapfenberg, Austria Filed: Apr. 26, 1972 Appl. No.: 247,576

Foreign Application Priority Data Germany 1. 2143302 Aug, 30, 1971 US.Cl. 164/252, 13/18 Int. Cl B22d 27/02 Field of Search 164/52, 252; 13/1851 Sept. 17, 1974 [56] References Cited UNITED STATES PATENTS 3,620,28711/1971 Medovar 164/52 Primary E.raminerJ. Spencer Overholser AssistantExaminer]ohn E. Roethel Attorney, Agent, or Firm-Arthur O. Klein 11Claims, 11 Drawing Figures ARRANGEMENT FOR USE IN MAKING SLAB INGOTS BYELECTRIC SLAG-REFINING This invention relates to a fusible electrodearrangement for use in the production of ingots by electricslag-refining in slab ingot molds. The flat or slab ingots made in suchingot molds are often required for the manufacture of flat products.

In the manufacture of such ingots, it is conventional to melt anelectrode having a rectangular cross-section in a rectangular ingotmold. The cross-sectional dimensions are selected so that there is auniform distance between the outside surfaces of the fusible electrodesand the inside surfaces of the ingot mold. Investigations which haveresulted in the present invention have shown that this electrodearrangement has the disadvantage that the temperature distribution ishighly nonuniform because the slag bath and particularly the mo]- tenmetal as well as the solidified portion of the ingot are cooled moreintensely adjacent to the narrow sides of the cross-section of the moldwhereas less heat is dissipated from the central portions of the longsides of the cross-section of the mold. Due to the differential supplyof heat to the walls of the ingot mold, the primary crystallizationvaries greatly in various parts of its cross-section.

This disadvantage caused by a non-uniform temperature distribution isalso inherent in other known fusible electrode arrangements. Forinstance, where three circular section electrodes are disposed onebeside the other in the ingot mold, the above-mentioned disadvantage iseven more pronounced. This is also the case where three electrodes areused which are rectangular in cross-section and have the same thickness.Only with I electrodes which are horizontally reciprocated along theaxis of symmetry which extends parallel to the long sides of therectangular cross-section of the ingot mold can the above-mentioneddisadvantage be avoided if a relatively long residence time is providedfor at the turning points, but this would involve a high structuralexpenditure.

It is an object of the invention to avoid said disadvantage. This objectis accomplished according to the invention by the use of one or moreelectrodes, which are horizontally spaced from the ingot mold wallswhich form the long sides of the horizontal cross-section by a largerdistance at the central portion of these ingot mold walls than at theedge portions of said walls to promote a uniform temperaturedistribution in the ingot as it solidifies. Because the electrodespacing increases as stated and its thickness decreases correspondinglyrelative to the thickness of the ingot, the slag layer area flownthrough by the electric current is decreased too. Hence, less heat isgenerated in the central portion of the cross-section of the ingot andthe heat is .generated there at a larger distance from the ingot moldwalls. The electrode arrangement according to the invention has also theadvantage that it can be adapted to all known circuit and electrodearrangements. Preferred embodiments are shown by way of example on theaccompanying drawing in top plan views.

FIG. 1 shows an arrangement comprising a single electrode disposed in arectangular ingot mold.

FIG. 2 shows an arrangement which comprises two electrodes in arectangular ingot mold.

FIG. 3 shows an arrangement comprising three electrodes in a rectangularingot mold.

FIGS. 4, 5 and 6 show arrangements comprising one, two, and threeelectrodes, respectively, which have curved surfaces spaced from thelong sides of the inside surfaces of the ingot mold;

FIG. 7 shows an arrangement which comprises one I-shaped electrode in arectangular ingot mold;

FIG. 8 shows an arrangement comprising three rectangular electrodes in arectangular ingot mold;

FIG. 9 shows an arrangement comprising one rectangular electrode in acurved ingot mold;

FIG. 10 shows an arrangement comprising three rectangular electrodes ina curved ingot mold; and

FIG. 1 1 shows an arrangement comprising two round electrodes and onerectangular electrode in a rectangular ingot mold.

The simplest embodiment comprises a single electrode, which is disposedin a rectangular ingot mold and has such a double-trapezoidalcross-section that the electrode has the smallest thickness at thecenter of its cross-section. This embodiment is shown in a top plan viewin FIG. 1 of the drawing. The spacing a of this electrode 1 from theingot mold walls 2 forming the long sides of the crosssection of theingot mold is not uniform but increases toward the center. The increaseof the spacing a is selected so that the average angle between the ingotmold wall and the surface of the electrode is about 2 to 8. Such aremelting plant may be supplied in known manner with single-phasealtemating current if the bottom plate and the electrode are connectedto respective output terminals of the transformer.

Another embodiment of the invention is shown in FIG. 2 and comprises twoelectrodes 1, which may be connected in parallel and supplied withsingle-phase alternating current. In this arrangement, any known powersupply system maybe employed, e.g., a supply from two separatetransformers or a supply from one transformer with the electrodes 1connected in series. In this embodiment, the distance a between theingot mold walls 2 and the electrodes 1 varies in the same manner as inFIG. 1.

If the remelting plant is arranged to be supplied with three-phase a.c.,an electrode arrangement as shown in FIG. 3 is recommendable, in whichthe distance a of the electrodes 1 differs only for the outer electrodes1, whereas the central electrode 1' is rectangular in crosssection. Theelectrodes are connected in known manner to the transformer forthree-phase alternating current.

It will be obvious to a person skilled in the art that the distancebetween the electrode and the ingot mold wall need not vary along astraight line or in a linear manner if the object of the invention is tobe accomplished. For instance, changes according to a curve arepossible, provided that the distance in the central portion is largerthan in the edge portions, as is shown in FIGS. 4, 5 and 6. FIG. 4 showsan arrangement according to the invention with a single electrode 1,FIG. 5 an arrangement with two electrodes and FIG. 6 one with threeelectrodes. All these embodiments exhibit a nonuniform change of thedistance a between the electrode and the ingot mold wall in that theelectrode crosssection is defined by a curve.

FIGS. 2 and 5 show examples in which the change spacing is changed onlyin part. Step changes of the spacing are also possible within the scopeof the invention. Such embodiments are illustrated by way of example inFIGS. 7 and 8 showing electrode arrangements comprising one and threeelectrodes, respectively.

It is also within the scope of the invention to change the horizontaldistance between the electrodes and the ingot mold walls which form thelong sides of the crosssection of the ingot mold by the use of ingotmold walls which are outwardly cambered on their inside surface. In thiscase, electrodes may be used which have a constant thickness at theiredge portions and in their central portion. Embodiments comprising acambered ingot mold are shown in FIGS. 9 and 10 with a singlerectangular electrode and three rectangular electrodes respectively. InFIG. 11 the outer electrodes are circular in cross-section and have alarger diameter than the thickness of the inner rectangular electrode.It will be understood that electrodes having a non-uniform thickness maybe combined with cambered ingot molds. Where ingot molds and/orelectrodes are used which have undulated surfaces, the mean spacing iscritical, ie, the lines passing through the waves at one-half of theheight thereof are considered as the boundaries of the cross-sections ofthe ingot mold and electrode or electrodes.

We claim:

1. An arrangement for use in making slab ingots by an electricslag-refining process, which comprises an ingot mold having insidesurfaces which define an elongated horizontal cross-section having longsides, each of said long sides having a central portion and outerportions, and

fusible electrode means extending in said ingot mold and horizontallyspaced from said inside surfaces at said central portions by a largerdistance than at said outer portions, all of said electrode means beingmovable with respect to said mold.

2. An arrangement as set forth in claim 1, in which said fusibleelectrode means comprise a single electrode. V

3. An arrangement as set forth in claim 1, in which said fusibleelectrode means comprise a plurality of electrodes.

4. An arrangement as set forth in claim 1, in which said inside surfacesdefine a rectangular horizontal cross-section and said fusibl'electrodemeans consist of a single electrode which'istrapezoidal and tapersinwardly in horizontal cross-section.

5. An arrangement as set forth in claim 1, in which said inside surfacesdefine a rectangular horizontal cross-section and said electrode meanscomprise an inner electrode which is rectangular in horizontalcross-section and disposed between said central portions and two outerelectrodes which are trapezoidal and taper inwardly in horizontalcross-section and disposed on opposite sides of said inner electrode.

6. An arrangement as set forth in claim 1, in which said inside surfacesdefine a rectangular horizontal cross-section and said electrode meanscomprise an inner electrode which is rectangular in cross-section anddisposed adjacent to said central portions and two outer electrodeswhich have a larger horizontal thickness than and are disposed onopposite sides of said inner electrode.

7. An arrangement as set forth in claim 6, in which said inside surfacesdefine a horizontal cross-section in which said long sides are outwardlycambered and said electrode means are of uniform horizontal thickness.

11. An arrangement as set forth in claim 1, in which said fusibleelectrode means comprises a pair of elec-.

trodes which are trapezoidally shaped and inwardly tapered in horizontalcross-section.

1. An arrangement for use in making slab ingots by an electric slag-refining process, which comprises an ingot mold having inside surfaces which define an elongated horizontal cross-section having long sides, each of said long sides having a central portion and outer portions, and fusible electrode means extending in said ingot mold and horizontally spaced from said inside surfaces at said central portions by a larger distance than at said outer portions, all of said electrode means being movable with respect to said mold.
 2. An arrangement as set forth in claim 1, in which said fusible electrode means comprise a single electrode.
 3. An arrangement as set forth in claim 1, in which said fusible electrode means comprise a plurality of electrodes.
 4. An arrangement as set forth in claim 1, in which said inside surfaces define a rectangular horizontal cross-section and said fusible electrode means consist of a single electrode which is trapezoidal and tapers inwardly in horizontal cross-section.
 5. An arrangement as set forth in claim 1, in which said inside surfaces define a rectangular horizontal cross-section and said electrode means comprise an inner electrode which is rectangular in horizontal cross-section and disposed between said central portions and two outer electrodes which are trapezoidal and taper inwardly in horizontal cross-section and disposed on opposite sides of said inner electrode.
 6. An arrangement as set forth in claim 1, in which said inside surfaces define a rectangular horizontal cross-section and said electrode means comprise an inner electrode which is rectangular in cross-section and disposed adjacent to said central portions and two outer electrodes which have a larger horizontal thickness than and are disposed on opposite sides of said inner electrode.
 7. An arrangement as set forth in claim 6, in which said outer electrodes are rectangular in horizontal cross-section.
 8. An arrangement as set forth in claim 7, in which said outer electrodes are square in horizontal cross-section.
 9. An arrangement as set forth in claim 7, in which said outer electrodes are circular in horizontal cross-section.
 10. An arrangement as set forth in claim 1, in which said inside surfaces define a horizontal cross-section in which said long sides are outwardly cambered and said electrode means are of uniform horizontal thickness.
 11. An arrangement as set forth in claim 1, in which said fusible electrode means comprises a pair of electrodes which are trapezoidally shaped and inwardly tapered in horizontal cross-section. 